The invention relates to a flat tube heat exchanger of the type having a plurality of flat tubes with flat sides and short sides that are rounded, and having zigzag fins that are internested in a sandwich-like fashion between the flat sides of the flat tubes, the fins having edges that are soldered to the flat sides of the flat tubes. A flat tube heat exchanger of this kind is known from German Patent Document A1-37 20 483 (FIG. 4), for instance. The invention also relates to a process for producing such a flat tube heat exchanger, the use of such a flat tube heat exchanger, and flat tubes for installation in the flat tube heat exchanger of the invention.
In such known flat tube heat exchangers (see also European Patent Disclosure B1-0 255 313, or the present Assignee's European Patent Disclosure A2-0 374 896), the short sides of the flat tubes are rounded with a semicircular arc whose radius equals half the distance d between the flat sides of a flat tube. This is the most frequently used embodiment of the short sides of flat tube heat exchangers, which are produced for various uses on a mass-production scale.
Zigzag fins and fins equivalent to them--hereinafter sometimes called merely fins for short--are internested laterally side by side in sandwiched fashion, in the following order: flat tube--(zigzag) fin--flat tube--(zigzag) fin--etc. This arrangement is not equivalent to inserting tubes into fins (usually provided with collars) in fin packages, where unlike the flat tube heat exchangers of the invention, the fins or their collars annularly surround the applicable tube (see British Patent Disclosure 538,018, for example); this last arrangement is therefore not addressed within the scope of the invention.
It is also known to embody the short sides of the flat tubes rectangularly, with rounded edges, or in gabled form with an obtuse angle at the apex of the gable. In all these cases, the zigzag fins are soldered only to the flat sides of adjacent flat tubes, and there is correspondingly the attempt to select the longest possible extension length of these flat sides. However, it does happen that the fins, soldered only to flat faces, will slip before the soldering. This not only interferes with the appearance of the heat exchange surface; it also increases its actual structural depth, and moreover may even cause problems in the heat-conducting connection between the flat tubes and the fins.
Moreover, the known profiling of the short sides of the flat tubes proves only limitedly streamlined in terms of the external heat exchanger fluid, such as an airflow, that sweeps through the fins.
Finally, when they are disposed in the engine compartment of a motor vehicle, the known profiles of the short sides of the flat tubes are sensitive to being struck by stones.